In the construction industry, tubular metal conduit frequently is used to provide a protective sheathing for electrical wiring. Typically, such conduit is used to route the wiring between junctions. To accommodate specific requirements of construction jobs and to carry wire between desired locations, the conduit must conform to walls and other architectural features and also circumvent obstacles. Because stock conduit typically is provided in linear portions, it often must be bent into various shapes to suit these purposes; however, when bending the conduit, it is important to avoid collapsing, crimping or deforming the conduit sidewalls to preserve the lumen within. This is necessary to prevent forming obstructions or restrictions in the conduit which might impede electrical wires or other objects which must pass through it and to avoid creating breaks or sharp angles in the conduit's interior surfaces. Such flaws must be avoided as they could cut or otherwise damage insulated wiring and result in fire or electrical hazards.
Electricians and construction workers frequently find it necessary to use many different sizes of conduit in any given construction project. In some instances, small conduit may be needed to carry relatively few wires through a narrow or tightly restricted area. In another application, however, an electrician may find that he needs to use a large diameter section of conduit to accommodate a large number of wires. In recognition of this need, commercial manufacturers provide electrical conduit in several standard sizes having various diameters and sidewall thicknesses. Each type of conduit has different bending properties which define the radius through which the conduit must be bent for satisfactory results. If bent too sharply, the conduit sidewalls will deform, causing buckling and possibly collapsing the conduit. One portion of conduit having a particular outside diameter but thick sidewalls will require bending at a different radius than another portion having the same diameter but thin sidewalls. In general, thin wall conduit must be bent into a curve having a radius that is greater than that permitted for rigid, or thick wall conduit, since thin wall pipe will buckle if it is bent through the smaller radius specified for rigid wall conduit. Thus, it is desirable that a pipe bender be versatile to accommodate the requirements of each type of conduit.
Pipe benders have been developed which have bending means specifically designed for each type of conduit. Typically, this has been accomplished by using an arcuate pipe receiving channel which conforms to the outside surface of conduit and which is formed into the radius required for bending one specific type of conduit. This type of pipe bender requires a different pipe receiving channel for bending each type and size of conduit. Also, to save time, effort, and expense, it is desireable that a single pipe bender be capable of bending many different sizes and types of conduit. Additionally, since electricians frequently wish to bend multiple sections of conduit simultaneously to expedite their work and to bend uniform sections of conduit which must be routed parallel to each other, it is desirable that a pipe bender have this capacity as well. These requirements have resulted in pipe benders having multiple pipe receiving channels, adaptations for different conduit sizes and wall thicknesses, and the capacity to bend multiple sections of pipe simultaneously. As enumerated below, however, certain limitations or otherwise undesirable characteristics historically have accompanied the incorporation of such improvements into pipe benders.
Pipe benders having multiple pipe receiving channels have been described in the following patents: Lidseen, U.S. Pat. Nos. 1,899,281; Parker, 2,695,538; Miller, 1,650,955; Martin, 1,949,938; Hautau, 3,147,792; and Van Den Kieboom, et al., 4,546,632.
The Lidseen '281 patent particularly relates to the type of portable conduit bender to which the present invention pertains. This patent shows a pipe bender arrangement having a single sheave block with three pipe receiving channels, all mounted on an axle protruding from one side of a mounting base. As a practical matter, such an arrangement is limited in its applications. Increasing the number of pipe receiving channels on the sheave block can be done only by adding additional pipe receiving channels to the outboard side of the rotatable sheave block. This increases the distance along the axle from the thus added pipe receiving channel to the mounting plate, so that when pipe is bent around such distal pipe receiving channels, the bending moment can become so great as to cause undue stresses at the juncture of the axle and the mounting plate. Such stresses can be damaging or destructive to the pipe bender, and in the past they have caused bending or even fracturing of the mounting plate through which the axle passes since they tend to "rip out" the sleeve or bearing supporting the axle. As a result, the sheave block of the Lidseen '281 arrangement cannot practically accommodate more than three pipe receiving channels.
In an attempt to overcome this inherent limitation, pipe benders of the type shown in the Lidseen '281 patent have been adapted to accept interchangeable pipe receiving channels which can be removed and replaced as desired for bending different types of sizes of pipe. Although the interchangeable pipe receiving channels increase somewhat the versatility of the pipe bender, their use necessarily incorporates the time consuming exercise of manually changing the pipe receiving channels. This interrupts the electrician's work, impedes the progress of the construction job, and decreases overall productivity.
In light of the aforementioned deficiencies, it is an object of the present invention to provide a new arrangement for a pipe bender which can accommodate a greater number of conduit sizes and types without relying on interchangeable pipe receiving channels and which can bend a greater number of pipes simultaneously.